In the field of surgery, and in particular ophthalmic surgery, there are known in the prior art many cutting instruments which are operated by electrical or pneumatic power. These devices are advantageous in that they increase the cutting rate and cutting force which the surgeon may wield. In addition, they generally allow the surgeon to perform delicate procedures more easily, in that the cutting instrument may be held steady without requiring manual or digital action to effect the cutting action.
One such device is a pneumatic scissors handpiece, otherwise termed an intraocular microscissors. In these devices a piston driven by pneumatic pulses is adapted to drive the scissor blades to open and close rapidly and repeatedly. Although this device is extremely useful, it does have serious drawbacks. One major failing is that the piston action is so rapid that it cannot be controlled to effect a partial closure of the blades. Partial closure of the scissor blades is frequently necessary. For example, when an ophthalmic surgeon is cutting the retinal membrane, one of the blades must be gradually inserted or "teased" under the membrane without damaging the underlying tissue, and the blades must be closed and opened gradually to prevent irreversible trauma to the retinal tissue. The pneumatically driven cutting instruments known in the prior art cannot perform this delicate procedure, as each pneumatic pulse causes the blades to close rapidly and completely and chop the tissue therebetween.
To overcome this deficiency in the pneumatically driven instruments, other automatic scissors arrangements have been devised using, e.g., a stepper motor coupled to a threaded member to close and open the scissor blades with greater proportional control. These devices suffer from poor control of the handpiece, due to the gyroscopic precessional force exerted by the rapidly rotating motor. Other devices use a cable-in-sleeve arrangement to operate the blades from a distant motive source. These instruments are imprecise, in that repositioning and other movement of the handpiece may alter the relationship of the cable and sleeve and cause unforeseen and undesirable closure of the blades. Thus there is no known power-operated surgical device in the prior art which is designed to perform gradual cutting, termed proportional cutting.